Various shapes and sizes of colloidal Co nanoparticles were fabricated by the polyol process using Co(acac)3, 1,2-hexadecanediol, oleylamine, and oleic acid within octylether. The rice-shaped Co nanoparticles with size of 30 nm and aspect ratio of 1.8 can be fabricated into a self-assembled form without assistance of surfactants. The addition of oleylamine as surfactant decreased the particle size and aspect ratio, and the addition of oleic acid made the surface of particle faceted without decreasing particle size from that of rice shape. The mixture of oleylamine and oleic acid produce differently shaped Co nanoparticles, including nanoprism, nanowire, and nanoflower according to the ratio of components, total amount of surfactant mixture, and reaction time. The fabricated nanoparticles showed ferromagnetic properties. These results showed that the various size and shape of metallic nanoparticles can be fabricated by the polyol process into controlled forms.